In manufacturing an integrated circuit (IC), films of desired semiconducting compounds, various oxides and other materials are plasma etched or deposited on a silicon wafer in layers, with each layer being etched according to a predetermined circuit pattern. The rate of etching varies with, among other things, the type of substance to be etched, the etching temperature, the power and frequency of RF (radio frequency) radiation in the etching chamber, the pressure inside the etching chamber, and the flow rate and composition of the gas that surrounds the wafer during the etching process. To manufacture consistent IC's, it is important to make these factors as consistent as possible. Changes in any of these factors can affect the etching process, including the etch rate, and a given change (such as an increase in temperature or RF power) will typically have similar effects on similar types of films.
A particularly elusive problem involves the leakage of atmospheric gases into the IC manufacturing system. Leaks are difficult to detect directly, but their effects on etching and deposition processes are significant.
When different IC's in a batch end up having different characteristics, such as layers of differing thicknesses, it is important to locate and standardize the factors that have caused the inconsistencies. Factors such as RF power and temperature can be measured directly with accurate instruments, and thus one can directly determine whether such factors are a source of problems.
When an IC is manufactured, a predetermined mixture of gases is flowed through the IC chamber at a given rate. Because of the difficulty in the detecting atmospheric leaks, which as a percentage of the total flow rate may be relatively low, it is difficult to directly identify such leaks as a source of IC inconsistencies. Such leaks can arise in many places in the system: the chamber itself, somewhere in the gas supply lines (such as at valves and connections), at structural defects in the chamber, etc. Gas mixture impurities may also be present in the sources of the gases themselves, even if the system is not leaking to atmosphere.
A system is therefore needed for isolating atmospheric leaks as a source of IC manufacturing problems, and in general for determining whether there are any impurities in a gas mixture used in the etching process.